This was an issue between my ex-wife and I. At least on my end. And there were no kids around, just lots of stress, and tiredness, and emotional issues, which created distance, so there was less desire, etc. We tried to keep a level of "intimacy", but it got to a point where even that was lacking. Because I never "fessed up" that it was way more important to me than it seemed to her (we'd talk about it on occasion, but her points about intimacy being more than sex, etc, were always so sincere, and I would try to see them, and accept them, etc), the problem only got worse. Until the desire was no longer there at all. I wanted her in my life, but needed more, and she deserved more than I was giving as well. Our breakup was not pleasant, and basically I just left because of the stress of the fertility issues and all that on top of everything else. The point is--sometimes, sex takes work. The less you have (especially women), the less you want...and then the less you have...and...it's a vicious cycle. Avoiding ruts is ideal, but if you find yourself in one, take the advice listed above: if the change is sudden, it could be an emotional/medical cause. If it's gradual, especially if it's just time/stress related, MAKE the time. Remember how good it feels. Remember how much of a connection you can feel when you really are intimate with someone. And aim for intimacy. Plan intimacy. If it leads to sex, which it very well might, that is a good thing. It will build (and/or rebuild) the bonds of love you feel. If not, you still have those moments of being deeply connected, and will look forward to the next time you get a chance to be with your SO like that again.